Dispersivity-induced crack patterns in soils subjected to combined wet-dry and freeze-thaw cycles: Insights from monitoring, testing, and CT scanning

Abstract

The unique climate in cold and arid regions facilitates soil crack initiation and propagation, which, in dispersive soils, further increases the risk of agricultural land degradation and ecological deterioration. This study investigated spatial crack development in dispersive soil subjected to wet-dry (WD) and wet-dry-freeze-thaw (WDFT) cycles, combining the results from temperature and humidity monitoring, physical property testing, and computed tomography (CT) scanning. The findings indicate that soil layers with developed cracks show greater fluctuations in volume water content during wetting and drying. During the wetting phase, upper-layer soil aggregates disperse into fine particles, which migrate downward through cracks with infiltration, changing the grain-size composition across layers. Fine particle accumulation hinders further water infiltration into deeper layers. In soil layers with developed cracks, the dry density of intact soil blocks increases. Cracks significantly enhance soil permeability, making it prone to instability under seepage. After ten WD cycles, the transverse-sectional crack ratio of the sample initially decreases and then stabilizes with increasing depth. Cracks extend vertically to approximately 7.5 cm and exhibit a horizontal, ring-like inward pattern. In the sample subjected to WDFT cycles, the transverse-sectional crack ratio shows two distinct peak values, and the crack development depth is about 9.0 cm. The combined effect of freezing and desiccation substantially increases the volume and connectivity of cracks, resulting in a marked difference in crack development at deeper layers. Compared to dry density and permeability coefficient, water content and grain-size composition more accurately reflect the early-stage crack development in dispersive soil.